Treated plastic articles (e.g., containing performance enhancing additives) can be prepared by means of incorporating (e.g., by means of compounding) additives directly into the polymeric materials from which the articles are prepared. Such direct (or bulk) incorporation methods result in the additive being dispersed substantially throughout the bulk of the plastic article.
Performance enhancing additives, such as UV stabilizers (absorbers), are typically expensive, and as such minimizing the amount incorporated into the plastic article while at the same time maintaining a sufficient level of performance is desirable. Direct incorporation methods are not particularly well suited with regard to minimizing the amount of performance enhancing additive used, as it is distributed throughout the whole of the plastic article. With direct incorporation methods, reducing the amount of performance enhancing additive throughout the bulk of the plastic article results in an equivalent reduction at the surface thereof, where it is typically most needed due to interactions of the surface with the environment (e.g., with light, oxygen, and/or the interior surfaces of a mold). As a result, physical properties of the plastic article are typically sacrificed if the amount of performance enhancing additive is too far reduced in a direct incorporation method.
The preparation of treated plastic articles by applying a treatment composition to the surface of the plastic article is generally known. Because the additives are incorporated primarily into the surface of the plastic article, such surface treatment methods are better suited with regard to minimizing the amount of performance enhancing additive used while at the same time maintaining a sufficient level of performance. Typically, the treatment compositions that are applied to the surface of the plastic article are non-aqueous.
In light of environmental concerns related to the use of organic solvents, more recently there has been increased emphasis towards the development of treatment methods that make use of aqueous treatment compositions. Methods of treating plastic articles by means of aqueous treatment compositions typically suffer from disadvantages that include, for example, non-uniform and/or inadequate treatment of the article, and an inconsistent degree of treatment/resulting physical properties between different batches of the same plastic articles.
U.S. Pat. No. 4,535,104 discloses a thermoplastic aromatic copolyestercarbonate article that is surface impregnated with a specific class of UV light degradation inhibiting compound. The '104 patent discloses dipping the thermoplastic copolyestercarbonate article into a non-aqueous solution of butoxy ethanol and UV stabilizer heated to a temperature of 125° C., followed by drying of the article at 150° C.
U.S. Pat. No. 4,323,597 discloses a method of preparing a ultraviolet radiation stabilized polymeric article (e.g., of polycarbonate) by applying to the surface thereof a composition containing ultraviolet radiation absorber and a non-aggressive liquid carrier. The '597 patent discloses examples of non-aggressive liquid carriers as including hydroxy ethers, alcohols, alcohol-water mixtures, liquid hydrocarbons and chlorofluorocarbons.
It would be desirable to develop new methods of treating plastic articles that make use of aqueous treatment compositions, and that result in the formation of uniformly and sufficiently treated articles. In addition, it would be desirable that such new methods also provide consistent degrees of treatment over time.